Conservator for liquid-immersed apparatus



Dec. 16, 1952 T C. LENNOX 2,622,122

CONSERVATOR FOR LIQUID-IMMERSED APPARATU S Filed March 31. 1950 Fig.1.

Inventor: Thomas C. Lennox,

His Attorney.

Patented Dec. 16, 1952 CONSERVATOR FOR- LIQUID-IMMERSED APPARATUS ThomasC. Lennox, Pittsfield, Mass assignor to General Electric Company, acorporation of New York Application March 31, 1950, Serial No. 153,174

3 Claims. 1

This invention relates to liquid-immersed electrical apparatus, and moreparticularly to expansion devices for the insulating liquid in whichsuch apparatus is immersed.

It is common practice to immerse certain types of electrical apparatus,such as electrical transformers, in an insulating liquid which partly orwholly fills .the container for the electrical apparatus, such as atransformer tank. Since such insulating liquid expands and contractswith changes in temperature of the electrical apparatus, it is necessaryto provide expansion space for the liquid. This expansion space may beprovided when the container for the electrical apparatus is normallyonly partially filled with the insulating liquid by making the containersufficiently large to accommodate the expansion of the liquid, analternative which is undesirable since it adds considerably to thecostof the apparatus, as well as unduly increasing its size.

The conventional means which has been used in the prior art forproviding for the expansion of the insulating liquid has been to use anauxiliary tank, commonly referred to as a conservator, which is mountedabove thecontainer for the apparatus, such as a transformer tank, andfeeds the insulating liquid to the tank by gravity. When the insulatingliquid in the main tank expands, it pushes a column of liquid up intothe conservator or expansion tank, which is made sufficiently large toaccommodate the anticipated expansion.

There are several undesirable features about the use of an expansion orconservator tank mounted above the main tank in which the apparatus iscontained, although, so far as I know, this is the usual way in whichconservator tanks have been mounted in the prior art. One seriousobjection is that such an arrangement increases the overall height ofthe electrical apparatus. A second objection when the insulating liquidis oil or some other inflammable liquid is that this arrangementincreases somewhat the fire hazard in the event that there should be anexplosion of the electrical apparatus, since the gravity feed from theconservator tank would continually add more fuel to the fire.

It is an object of this invention to provide a new and improved liquidexpansion tank construction for use with liquid-immersed electricalapparatus.

It is a further object of thisinvention to provide a liquid expansiontank for use'with liquidimmersed electrical apparatus which will reducethe necessary overall height of the apparatus.

In accordance with these objectives, this invention provides anexpansion tank which is mounted on the side of the containing tank forthe electrical apparatus, and maintains the oil within the main tank ata substantially constant level by utilizing the heating and coolingcycle of the electrical apparatus to produce the necessary motion of theinsulating liquid to and. from the expansion tank.

Hereinafter in this specification I shall use a transformer by way ofexample as the type of liquid-immersed electrical apparatus to which myinvention is applied. However, it will be understood that my inventionapplies equally well to any type of tank-enclosed liquid-immersedapparatus. Furthermore, in referring to the insulating liquid whichsurrounds the electrical apparatus, I shall hereinafter use oil by wayof example as the insulating liquid used although it will be understoodthat any other suitable insulating liquid may be used.

The features of this invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself, however,both as to its organization and use, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFig. 1 is a form of my invention utilizing a side-mounted expansiontank, with the transformer tank and expansion tank both being sealedagainst the admission of air from the atmosphere; while Fig. 2 is amodification of the structure shown in Fig. 1 in which the connectingduct between the main transformer tank and the expansion tank is placedbelow the top of the main transformer tank.

There is shown in Fig. 1 a form of my invention in which the completetransformer tank and expansion tank system is sealed and is not open tothe atmosphere, and in which the transformer tank is completely filledwith oil. There is shown in Fig. 1 a transformer tank 20 of conventionaldesign having a duct 2| communicating with the inside of the transformertank and mounted above the cover of the tank. The duct 2| extendsradially outwardly beyond the outer periphery of the tank 20 and isconnected by a pipe 22, which extends parallel to the axis of tank 20,to an expansion chamber 23 which is mounted on-the side, of tank 20. Thesystem is filled with. oil

through a suitable valve (not shown) in the bottom of tank 20 until tank20 is full and sufiicient oil has flowed through duct 2! and pipe 22 tofill expansion tank 23 to the normal oil level which 3 it is desired tomaintain in expansion tank 23 at the temperature of filling, such as theoil level indicated by the dotted line 24, for example. Sufficient air,or preferably nitrogen, should be forced into the top of the expansiontank 23 above the oil level so that When the minimum operatingtemperature is reached, the pressure inside the expansion tank willstill be slightly above atmospheric. As the oil in the transformer tankexpands under high temperature conditions, it will force oil through theduct 2| and conduit 22 into expansion chamber 23. Any

excess air or gas in the top of the tank 20 is ex pelled in advance ofthe expulsion of the oil. When the temperature inside transformer tank20 declines in value the pressure of the air or nitrogen above the oillevel in expansion chamber 23 will force oil back up through pipe 22 andinto tank 26. When this happens, the oil in the expansion chamber willdiminish to a low level such as is indicated by the dotted line 25.Transformer tank 20 is maintained completely filled with oil at alltimes, with the thermal cycle of the transformer maintaining a flow ofoil be.- tween the main tank and expansion tank in accordance with theexpansion and contraction of the oil. An oillevel indicator or alarm 4|is provided in duct 2| to warn of loss of oil through leakage.

Since this transformer and expansion tank system is not open to theatmosphere, means should preferably be provided to prevent rupture ofthe main tank 20 in case of an excessive pressure condition in thetransformer tank-expansion tank system. Since a simple pressure reliefdiaphragm on top of the main tank 20 would, if broken, permit thepressure of the air or nitrogen inside expansion tank 23 to force allthe oil in expansion tank 23 out through the broken diaphragm, such anarrangement is unacceptable. In order to provide an adequate pressurerelief, I provide a double. diaphragm arrangement, as shown in Fig. 1.These two diaphragms are indicated at .26 and 21, respectively.Diaphragms 26 and 2.1 are located in an extension of duct 2|, and areradially displaced from one another. It will be noted that due to theirradial displacement along the. extension of duct 2|, diaphragms 26 and21 enclose a small space 23 which is connected' by a conduit 29 to theair or nitrogen space above the oil level in expansion tank 23. Thespace 28 is therefore at the same pressure as the space above the oillevel inside expansion tank 23. In the event of a moderate increase inpressure beyond the allowable pressure limit inside expansion tank 23,radially outer diaphragm 21 will be caused to rupture, thereby relievingexcess pressure. However, in the case of a. very sudden increase inpressure inside expansion tank 23 which could notbe relieved by the flowof oil through pipe 22 or ga through the conduit 29, both diaphragms 25and 21 will rupture.

Preferably diaphragm 27 will be weaker than diaphragm 26. This is sothat in the event of a moderate increase in pressure beyond theallowable pressure limit inside expansion tank 23, rupture of diaphragm21 will relieve the excess pressure but diaphragm 26 will still beintact to prevent loss of the oil in duct 2 I.

A basket of silica gel 30 may be suspended in the upper part ofexpansion chamber 23 to absorb any residue of free moisture left in thesystem at installation.

Thereis shown in Fig. 2 a modificat n f the construction of Fig. 1 whichpermits the use of a small gas cushion in the top of the maintransformer tank as a protection against sudden increases in pressure.In Fig. 2 there is shown a transformer tank 3| which is filled to an oillevel 32 slightly below the top of the tank to permit a gas or aircushion 33 between the oil level 32 and the topof tank 3|. A duct 34communicates with tank 3| at a level slightly below the top of the tank,the oil level in the duct being the same as in the tank. A pipe 35parallel to the axis of tank 3 I. provided for oil flow between thetransformer tank 3| and expansion tank 36 which is similar to expansiontank 23 shown in Fig. 1.

The systemisfilled with oil through a suitable valve in the bottom oftank 3| until the oil in tank 3| has reached a level slightly below thetop of the tank, and suflicient oil has flowed through duct 34 andconduit 35 to fill expansion tank 36 to the normal oil level which it isdesired to maintain in the expansion tank 36 at the temperature. offilling. Sufiicient air, or preferably nitrogen, should beforced intothe top of expansion tank 36 above the oil. level, and into the space3.3 above the oil level in transformer tank 3|, so that when the minimumoperating temperature is reached the pressure inside the system willstill be slightly above atmospheric. In order to provide adequatepressure relief, a double diaphragm arrangement imilar to that of Fig. 1is provided. Diaphragms 31 and 38 are located in an extension of duct34, and are radially displaced from one another. Due to their radialdisplacement from one another along the extension of duct 34,,diaphragms 31 and 33 enclose a small. space 39 which is connected by aconduit 40 to the air or nitrogen space above the oil level in expansiontank 36. The space 39 is therefore at the same pressure as the spaceabove the oil level inside expansion'tank 35. In the event of a moderateincrease in pressure beyond the allowable pressure limit, radially outerdiaphragm 38 will. be caused to rupture, thereby relieving, theexcessp'ressure. However, in case of a very sudden increase in pressurewhich could not be relieved by the flow of oil or gas through theconduits 35 and 40, both diaphragms 31 and 38 will rupture.

Since duct 34 islocated below the top of transformer tank 3|, and theoil level in the duct is the same as the oil level in the tank 3|, ifthe diaphragms 31 and 38 were located at the same level as the oil, anexcessive loss of oil would occur if both diaphragms 31 and 38 ruptured.In order to prevent such an excessive loss of oil, the radially outerportion of duct 34 containing diaphragms 31 and 38 is elevated above theoil lever 32. This assures that in the event of rupture of the.diaphragms 3'! and, 38 only oil above the level indicated by dotted line32 will gene ally be'lost. through the diaphragms. Oil level indicatoror alarm is provided to warn of decrease of oil level due to leakage orother causes.

While there, have been shown and described particular embodiments of myinvention, it will be obviousto those skilled in the art that variouschanges and modifications can be made therein without departing fromtheinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to secure by Letters. Patent of theUnited States is:

1. In combination with liquid-immersed elecca a p ratus n a containingtank, expansion means for said liquid comprising an expansion tankmounted exteriorly adjacent said containing tank, substantially thegreater portion of said expansion tank being lower than the uppermostsurface of said containing tank, a duct positioned above the top surfaceof said containing tank and projecting radially outwardly from saidcontaining tank, one end of said duct being connected to the interior ofsaid containing tank, the other end of said duct being provided withpressure-relief means, said duct being connected intermediate its twoends to a conduit projecting into said expansion tank substantially tothe bottom of said expansion tank, said containing tank normally beingcompletely filled with said liquid, said containing tank and saidexpansion tank being sealed against entrance of air from the atmosphere,said expansion tank being filled above any liquid present therein with agaseous medium at a minimum pressure in excess of atmospheric pressure,the normal heating and cooling cycle of said liquid-immersed electricalapparatus causing pressure differentials between said containing tankand said expansion tank which result in liquid flow between said twotanks, said pressure relief means comprising a first and a secondfrangible diaphragm positioned in said radially-projecting duct, saidtwo diaphragms enclosing a space at the radially outer end of said duct,a conduit connecting said space between said diaphragms to the upper endof said expansion tank, excessive gas pressure interiorly of saidexpansion tank normally causing the radially outermost of saiddiaphragms to rupture before said radially inner diaphragm ruptures.

2. In combination with liquid-immersed electrical apparatus in acontaining tank, expansion means for said liquid comprising an expansiontank mounted exteriorly adjacent said containing tank, substantially thegreater portion of said expansion tank being lower than the uppermostsurface of said containing tank, said containing tank being filled withsaid liquid to a level slightly below the top of said containing tank, agaseous medium filling the space between the top level of said liquidand the top of said containing tank, a duct projecting radiallyoutwardly from said containing tank, one end of said duct beingconnected to the interior of said containing tank, the other end of saidduct being provided with pressure-relief means, said duct beingconnected intermediate its two ends to a conduit projecting into saidexpansion tank substantially to the bottom of said expansion tank, saidcontaining tank and said expansion tank being sealed against entrance ofair from the atmosphere, said expansion tank being filled above anyliquid present therein with a gaseous medium at a minimum pressure inexcess of atmospheric pressure, the normal heating and cooling cycle ofsaid liquid-immersed electrical apparatus causing pressure differentialsbetween said containing tank and said expansion tank which result inliquid flow between said two tanks, said pressure-relief meanscomprising a first and a second frangible diaphragm positioned in saidradially projecting duct, said two diaphragms enclosing a space at theradially outer end of said duct, a conduit connecting said space betweensaid diaphragms to the upper end of said expansion tank, excessive gaspressure interiorly of said expansion tank normally causing the radiallyoutermost of said diaphragms to rupture before said radially innerdiaphragm ruptures, the radially outer portion of said duct in whichsaid diaphragms are contained being elevated above the normal liquidlevel present in said containing tank.

3. In combination with liquid-immersed electrical apparatus in acontaining tank, expansion means for said liquid comprising an expansiontank mounted exteriorly adjacent said containing tank, substantially thegreater portion of said expansion tank being lower than the uppermostsurface of said containing tank, a duct having one end connected to theinterior of said containing tank at the upper end thereof and projectingradially outwardly from said containing tank, the other end of said ductbeing provided with pressure-relief means, said duct being connectedintermediate its two ends to a conduit projecting into said expansiontank substantially to the bottom of said expansion tank, said containingtank and said expansion tank being sealed against entrance of air fromthe atmosphere, said expansion tank being filled above any liquidpresent therein with a gaseous medium at a minimum pressure in excess ofatmospheric pressure, the normal heating and cooling cycle of saidliquidimmersed electrical apparatus causing pressure differentialsbetween said containing tank and said expansion tank which result inliquid fiow between said two tanks, said pressure relief meanscomprising a first and a second frangible diaphragm positioned in saidradially projecting duct, said two diaphragms enclosing a space at theradially outer end of said duct, a conduit connecting said space betweensaid diaphragms to the upper end of said expansion tank, excessive gaspressure interiorly of said expansion tank normally causing the radiallyoutermost of said diaphragms to rupture before said radially innerdiaphragm ruptures.

THOMAS C. LENNOX.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,584,523 Egbert May 11, 19261,693,265 Austin Nov. 27, 1928 1,693,430 Austin Nov. 27, 1928 1,697,141Rodman et al. Jan. 1, 1929 1,712,765 Hill May 14, 1929 1,775,028Hilliard Sept. 2, 1930

